The general objective of this proposal is to develop continuum mechanics in pulmonary physiology, to obtain a better understanding of the mechanical basis of ventilation and perfusion of the lung. Specifically, the following projects will be done: (1) Determination of the elasticity of small pulmonary arteries and veins. (2) Elasticity of pulmonary arterioles and venules. (3) The constitutive equations of pulmonary blood vessel wall. Mathematical representation of the pseudoelastic stress-strain relationship. (4) Interdependence of blood vessels and parenchyma - the tethering of arteries and veins by interalveolar septa. (5) Patency of pulmonary veins under negative pressure, with specific applications to blood flow in zone 2 condition (in which the alveolar gas pressure is smaller than the pressure in the pulmonary artery but larger than that in the vein.) (6) Elasticity of the lung parenchyma. (7) Determination of the material constants of the lung tissue elasticity. (8) Experimental measurement of the distortion of pulmonary alveoli when the parenchymal tissue is subjected to nonuniform anisotropic stress states. (9). The collagen and elastin networks in the interalveolar septa, their experimental determination and theoretical analysis. Thus, by completing this research we will obtain reasonably complete information about the mechanical properties of pulmonary blood vessels and parenchyma, their interdependence and relationship to the microscopic alveolar structure and fibroprotein network in the tissues. With this information the physiological problems of blood flow and stress and strain distribution in the lung, and the stability of the lung will be analyzed.